This invention relates generally to thermal insulation and more particularly to a method for providing a thermal insulation structure suitable for refrigeration applications.
As it is known in the art, a method currently used for providing thermal insulation in refrigeration appliances is to use foam insulation, such as polyurethane foam. Foam insulation contains chlorofluorocarbons (CFCs) which have been discovered to be environmentally damaging. The Environmental Protection Agency is mandating a reduction in future use of CFCs. Further, strict new standards are being promulgated regarding energy consumption by the Department of Energy. As a result of these emerging requirements, manufacturers of refrigeration products are extending substantial efforts in order to provide alternative insulation structures which would reduce the use of CFCs and improve the energy efficiency of refrigeration appliances.
One technology known in the art that appears promising toward meeting these goals, is the use of evacuated panel insulation in which a powdered material having a relatively large capacity to adsorb gases is compressed and enclosed within a container made of a material having relatively low permeability to gases. The container is evacuated to provide a panel having suitable thermal insulation properties for use in refrigeration applications. The panels thus provided are relatively rigid and may be easily arranged in refrigeration products, such as in the door and walls of a refrigerator.
As it is further known in the art, evacuated panel insulation, like other thermal insulation structures, should contribute to providing refrigeration appliances with several desirable characteristics such as relatively low energy consumption, a long expected life, and manufacturing economic feasibility. Energy consumption of refrigeration appliances is based on, inter alia, the thermal conductivity of the insulating material which is related to conductive heat transfer. In the case of an evacuated panel, long-term thermal performance is based on the ability of the insulation to adsorb gases or getter. Such gettering reduces interstitial gas pressure, thereby reducing heat transfer by convection. The expected life of the refrigeration appliance is dependent on the expected insulation life and, generally, refers to the time duration over which the appliance operates without significant degradation in energy consumption. Manufacturing economic feasibility encompasses several factors such as material cost, equipment cost, ease of manufacture, and production time.